China’s senior diplomat in Britain, Liu Xiaoming, has a reputation for undiplomatic remarks. The ambassador’s infamous likening of Japanese prime minister Shinzo Abe’s government to Lord Voldemort, Harry Potter’s threatening nemesis, did little to ease historical bilateral tensions between the two countries. His blunt remarks last week about the delay to the Hinkley Point nuclear power station project ordered by Theresa May also jarred badly.

Liu put the government on notice that cancellation of the troubled £18bn scheme, in which the state-owned company, China General Nuclear Power (CGN), has (or would have) a 33% stake, could have serious, negative consequences for wider trade, investment and political relations between Britain and China. His warnings about damaged “mutual trust” and a “critical juncture” sounded less like the counsel of a friend, more like the threats of a bully.

There was a time, not so long ago, when ill-considered public comments by a senior Chinese official might have been safely ignored. Britain was often the target of vituperative abuse in the period leading up to the Hong Kong handover in 1997. Chris Patten, the last British governor, still bears the scars. The pressure did not discernibly affect government policy. But times change and so, too, does the balance of power, which has swung decisively in China’s favour in the succeeding two decades. Britain needs China now in ways it did not in the past.

This does not mean insulting or threatening behaviour is any more acceptable. But it does mean that May will feel obliged to give serious weight to China’s concerns over Hinkley when a final decision is made next month. Similar pragmatic calculations lay behind the ingratiating welcome afforded Xi Jinping, China’s unelected Communist leader, in London last autumn, and the former chancellor George Osborne’s myopic championing of a lucrative new “golden era” in Sino-British ties. If it is to prosper in a globalised 21st century prospectively dominated by China and other emerging powers such as India, Britain must, to some degree, kowtow to Beijing.

In recent years, China has invested more capital in Britain than in any other EU country. As an export market, its potential is unmatched. Britain, meanwhile, despite all Osborne’s austerity, is deeply in debt and living beyond its means. As Stephen King of HSBC put it: “If the Chinese turn their backs on us, then we’ll have to tighten our belts even further, particularly if we’re given a frosty reception by the Chinese-sponsored Asian Infrastructure Investment Bank, reducing the opportunities for British business to operate within the world’s most dynamic region.”

But this changed reality is also partly the product of choices freely entered into. By voting to leave the EU, Britain has made an additional rod for its back. Brexit will exacerbate Britain’s vulnerability, both economic and political, in a dangerous world where, as Mark Carney, the Bank of England governor, rightly says, it depends increasingly on the kindness of strangers. As we have argued in the past, it may be time, as American and west European power fades, for countries such as China to shape a new world order. Who knows, they may eventually do a better job. It would not be difficult.

Yet it is also true that China’s one-party system, its huge democratic deficit, its lack of transparency, its disregard for human rights, religious freedoms and international legal norms, and yes, its leaders’ tendency towards bullying are sharply at odds with British values, standards and policy aims. The Hinkley decision has suddenly been rendered more fraught by US allegations of industrial espionage involving CGN and by Australia’s refusal, on grounds of security, to allow Chinese control of a key energy asset.

This tension between who we are and who we do business with has always been present. A good example in recent decades has been Britain’s close and controversial collaboration with oil-rich Saudi Arabia. But corrupting though the alliance with Riyadh was, it did not fundamentally change Britain’s worldview. The case is altered now. Our wilful undermining of our key European alliances means that over time, Britain, alone, may struggle to stand up to the likes of China, defend its values and maintain relationships based on mutual respect. There will be more Hinkleys. The effect could be highly corrosive.

In the big, bad, lonely world beyond Brexit, predators of many varieties roam. Last week saw a reminder from the incorrigible Vladimir Putin, Russia’s president, that the Crimea crisis of 2014 is far from over and that the war in Ukraine could reignite at any moment. The particulars of the latest flare-up are less significant than the fact that Putin again appears ready to place European security at hazard, just as his actions regularly challenge Nato, his bombers and helicopter gunships murder civilians in Aleppo and his sports officials blithely ignore international doping rules.

Surely nobody is sensibly suggesting Britain, in a fit of panicky, post-Brexit international outreach, should try to bury its differences with the reckless, lawless regime in Moscow, notwithstanding last week’s embarrassing telephone calls to the Kremlin by May and Boris Johnson, the foreign secretary. Putin, after all, stands accused by an official British inquiry of direct complicity in the murder of Alexander Litvinenko, the former KGB agent poisoned with polonium in London. If Putin were an African leader, there would be calls for him to be investigated by now by the International Criminal Court for possible war crimes in Syria, Ukraine and Chechnya.

Yet the question nevertheless arises: how does Britain, no longer working in close concert with France, Germany and Poland, propose to manage the Russian problem? Will Moscow, like China sensing weakness and uncertainty, be tempted to pressure and bully May’s untested government, even as armed forces chiefs warn they are outgunned by the Russians? Will May try to win Putin round or will she confront him? Her first test comes next month at the G20 summit in China. One thing is already certain: the hapless Johnson is no match for Sergei Lavrov, his veteran counterpart. A Lavrov-Johnson summit would be like inviting a wolf to take tea with a tethered goat.

Brexit’s champions promised to forge a range of post-Brussels international relationships, thereby creating a more vibrant, prosperous Britain. China and Russia show just how perilous and problematic this project is. History suggests Britain can look to the US for succour and support. But with American confidence failing, and a weird Trumpian dystopia taking root, even that fall-back seems in jeopardy.